1. Field of the Invention
The present invention relates to a method of producing an organic-inorganic composite material formed from an organic polymer and a metal alkoxide, an organic-inorganic composite material obtained by this method, and a laminate thereof.
2. Related Art
Inorganic materials such as metal and ceramics are excellent in heat resistance, mechanical strength, electrical properties, optical properties, chemical stability etc., and used widely in industry by utilizing these properties. However, these materials are generally highly brittle and rigid, and their use may be limited because work or mechanical processing at a high temperature is necessary for working them into a desired shape.
On the other hand, organic polymers are excellent in workability and have flexibility, so that they can be easily worked into a desired shape. However, the organic polymers are often inferior to the inorganic materials in heat resistance and chemical stability.
Hence, attention is attracted in recent years to an organic-inorganic composite material comprising an inorganic material and an organic polymer material to attain the properties of the two.
As the composite material of an organic polymer and an inorganic material, a composite material having an inorganic material in a fibrous or powdery form dispersed in an organic polymer material has been used in various fields. In recent years, there is extensive development of an organic-inorganic nano-composite material (also called an organic-inorganic hybrid material) in which organic and inorganic regions are compounded at the nanometer level or molecular level.
Because the organic and inorganic regions can be dispersed at the nanometer level or molecular level, the organic-inorganic nano-composite material is used as a material for electronic components or as a material for mechanical components. Further, the organic or inorganic region in the material can be designed to be smaller than light wavelength, thus making light absorption and scattering low. Accordingly, the organic-inorganic nano-composite material has been studied to be used as a material for optical waveguide, optical fiber, or the like by providing optical transparency.
Methods of producing organic-inorganic composite materials are disclosed in xe2x80x9cStructure of poly(vinylpyrrolidone)xe2x80x94silica hybridxe2x80x9d, Motoyuki Toki, et al., Polymer Bulletin 29, 653-660 (1992) and in xe2x80x9cOrganic-inorganic hybrid sol-gel materials, 1xe2x80x9d, Jen Ming Yang, et al., Die Angewandte Makromolekulare Chemi 251 (1997) 49-60 (Nr. 4356) etc.
However, the production methods described in these literatures have a problem that organic-inorganic composite materials excellent in optical transparency cannot be obtained.
When the organic-inorganic nano-composite material is used as an optical waveguide, its light transmission layer is often formed on a substrate. In this case, the adhesion of the substrate to the light transmission layer is important.
For the purpose of improving the adhesion, it has been attempted to provide a graded structure with the material by continuously changing its composition.
For example, in Japanese Patent Laid-Open No. 34413(2000), proposed is a silica/polycarbonate-based composite material wherein the concentration of silica is continuously changed by applying successively a plurality of coating solutions different in the composition of organic and inorganic components on a substrate.
Further, in Japanese Patent Laid-Open No. 336281(2000), proposed is a graded structure prepared by applying a coating solution consisting of a mixture of an organic polymer and a metal compound capable of forming a metal oxide by hydrolysis on an organic substrate, then heating and drying it, the graded structure having a higher content of the organic component at the side of the substrate and a higher content of the inorganic component in the vicinity of the surface.
However, the methods proposed in the publications described above have a problem that the adhesion of the light transmission layer to the substrate cannot be sufficiently improved.
A first object of the present invention is to provide a production method capable of producing an organic-inorganic composite material excellent in optical transparency, as well as an organic-inorganic composite material obtainable by this method.
A second object of the present invention is to provide a light transmission structure having a light transmission layer with improved adhesion to a substrate.
The production method of the present invention is a method of producing an organic-inorganic composite material formed from an organic polymer and a metal alkoxide, which comprises the steps of polycondensating a metal alkoxide through hydrolysis until the unreacted metal alkoxide is reduced to 3 vol. % or less, and mixing the polycondensated metal alkoxide with an organic polymer to form an organic-inorganic composite material.
In the present invention, a metal alkoxide is polycondensated through hydrolysis until the unreacted metal alkoxide is reduced to 3 vol. % or less, and the polycondensated metal alkoxide is mixed with an organic polymer to form an organic-inorganic composite material. The obtained organic-inorganic composite material is excellent in optical transparency. Thus, according to the present invention, an organic-inorganic composite material suitable as a material for optical component such as optical waveguide or optical fiber can be produced.
The metal alkoxide used in the present invention includes alkoxides of metals such as Si, Ti, Zr, Al, Sn and Zn. In particular, Si, Ti or Zr alkoxide is preferably used. Accordingly, alkoxy silane, titanium alkoxide and zirconium alkoxide are preferably used, and particularly alkoxy silane is preferably used. The alkoxy silane includes tetraethoxy silane, tetramethoxy silane, tetra-n-propoxy silane, tetraisopropoxy silane, tetra-n-butoxy silane, tetraisobutoxy silane, phenyltriethoxy silane, phenyltrimethoxy silane, 3-methacryloxypropyltriethoxy silane, and 3-methacryloxypropyltrimethoxy silane.
The organic polymer in the present invention is not particularly limited insofar as it forms an organic-inorganic composite material with a metal alkoxide. The organic polymer includes, for example, polyvinylpyrrolidone, polycarbonate, polymethylmethacrylate, polyamides, polyimides, polystyrene, polyethylene, polypropylene, epoxy resins, phenol resins, acryl resins, urea resins, melamine resins etc. From the viewpoint of formation of the organic-inorganic composite material excellent in optical transparency, polyvinylpyrrolidone, polycarbonate, polymethylmethacrylate, polystyrene or a mixture thereof is used preferably as the organic polymer.
Hydrolysis of the metal alkoxide is conducted preferably in the presence of water for hydrolysis and an acid as a catalyst for hydrolysis. The molar ratio of water for hydrolysis to the metal alkoxide (water/metal alkoxide ratio) is preferably from 1.0 to 3.0, more preferably from 1.5 to 2.5. The acid used as a catalyst for hydrolysis includes inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid, as well as organic acids, and particularly hydrochloric acid is preferably used. The molar ratio of hydrochloric acid to the metal alkoxide (hydrochloric acid/metal alkoxide ratio) is preferably from 0.001 to 0.5, more preferably from 0.001 to 0.01, particularly preferably 0.002.
The amount of the unreacted metal alkoxide, that is, the amount of the remaining metal alkoxide, can be measured by gas chromatography etc. The reaction time in which the amount of the remaining metal alkoxide is reduced to 3 vol. % or less is previously determined by hydrolyzing the metal alkoxide under predetermined conditions of temperature, concentration etc., and for the determined reaction time, the metal alkoxide is hydrolyzed and polycondensated, and then mixed with an organic polymer to form an organic-inorganic composite material. Alternatively, the amount of the unreacted metal alkoxide may be measured every time the composite material is formed.
The organic-inorganic composite material of the present invention is characterized by being produced by the production method of the present invention described above. The organic-inorganic composite material of the present invention can be formed for example by preparing a mixed solution of a solution of hydrolyzed and polycondensated metal alkoxide and an organic polymer and then applying the mixed solution. Such a coating solution can be applied onto a substrate to form an organic-inorganic composite material on the substrate. As the substrate, a substrate composed of an organic or metal material can be used. When the organic-inorganic composite material of the present invention is used as an optical material, the organic-inorganic composite material may be formed on a transparent substrate.
When the organic-inorganic composite material of the present invention has a thickness of 10 xcexcm, it can exhibit 90% transmittance of light of a wavelength of 600 to 1000 nm. The content of the metal element in the organic-inorganic composite material of the present invention is preferably 0.1 to 46 wt. %, more preferably 5 to 37 wt. %.
The laminate of the present invention has a structure wherein the organic-inorganic composite material produced by the above-described production method of the present invention is laminated. For example, a plurality of mixtures different in the content of metal alkoxide can be applied one after another to form a laminate having a different content of metal alkoxide in each layer.
The laminate in the first aspect of the present invention has a concentration gradation wherein the metal element of the metal alkoxide is increased or decreased from one side to the other side of the laminate. Generally, the refractive index of the organic-inorganic composite material can be changed by changing the concentration of the metal element in the organic-inorganic composite material. Accordingly, the laminate in the first aspect of the present invention can be provided with a graded structure in which refractive index is increased or decreased from one side to the other side of the laminate by grading the concentration of the metal element. The laminate having this graded structure can be used as a material for opticalcomponents such as optical waveguides and optical fibers.
The laminate in the second aspect of the present invention has a concentration gradation wherein the metal element of the metal alkoxide is first increased and then decreased from one side to the other side of the laminate. Accordingly, the laminate in the second aspect of the present invention can be provided with a graded structure in which refractive index is first decreased and then increased from one side to the other side of the laminate.
The laminate in the third aspect of the present invention has a concentration gradation wherein the metal element of the metal alkoxide is first decreased and then increased from one side to the other side of the laminate. Accordingly, the laminate in the third aspect of the present invention can be provided with a graded structure in which refractive index is first increased and then decreased from one side to the other side of the laminate.
Like the laminate in the first aspect, the laminates in the second and third aspects can be used as a material for optical components such as optical waveguides or optical fibers insofar as they have the above-described structure of graded refractive index.
The light transmission structure of the present invention comprises a metallic substrate, a metal oxide layer arranged on the substrate, and a light transmission layer composed of an organic-inorganic composite material provided on the metal oxide layer.
In the present invention, the metal oxide layer is arranged between a substrate and a light transmission layer composed of the organic-inorganic composite material. By arranging the metal oxide layer, the adhesion of the light transmission layer to the substrate can be improved.
The substrate in the present invention is not particularly limited insofar as it is made of a metal, and is exemplified by a substrate made of Si, Al, Ge, Cu, Fe, Ni, Zr, Sn, Zn or Ti.
The metal oxide layer is preferably an oxide layer containing at least one element contained in the substrate. For example, when the substrate is a silicon substrate or a silicon alloy substrate, the metal oxide layer is preferably a Si oxide layer.
The thickness of the metal oxide layer is preferably 5 nm to 20 xcexcm, more preferably 50 nm to 5 xcexcm. If the metal oxide layer is too thin, the effect of improving adhesion may not be sufficiently achieved, while if the metal oxide layer is too thick, the adhesion may be lowered due to stress upon formation of the metal oxide layer itself.
The method of forming the metal oxide layer in the present invention includes, but is not limited to, reactive vapor deposition, sputtering, CVD, and PVD. Alternatively, the metal oxide layer may be formed by heating oxidation, a sol-gel process of hydrolyzing and polycondensating a metal alkoxide, or a wet process such as anodization. The metal oxide layer may also be formed by exposing a substrate to the air or an oxygen gas for a long time.
The light transmission layer in the present invention is composed of the organic-inorganic composite material formed from an organic polymer and a metallic compound. The thickness of the light transmission layer is preferably 4 to 500 xcexcm, more preferably 5 xcexcm to 50 xcexcm.
When the organic-inorganic composite material is to be formed from an organic polymer and a metal alkoxide, the metal alkoxide is polycondensated through hydrolysis until the unreacted metal alkoxide is reduced to 3 vol. % or less, and then mixed with an organic-inorganic polymer to form an organic-inorganic composite material. An organic-inorganic composite material excellent in optical transparency can be thereby formed. The amount of the unreacted metal alkoxide can be measured by using gas chromatography etc. The reaction time in which the amount of the remaining metal alkoxide is reduced to 3 vol. % or less is previously determined by hydrolyzing the metal alkoxide under predetermined conditions of temperature, concentration etc., and for the determined reaction time, the metal alkoxide is hydrolyzed and polycondensated, and then mixed with an organic polymer to form an organic-inorganic composite material. Alternatively, the amount of the remaining metal alkoxide is measured while the metal alkoxide is hydrolyzed and polycondensated, and once the amount is reduced to 3 vol. % or less, the metal alkoxide may be mixed with an organic-inorganic polymer.
The content of the metal element in the organic-inorganic composite material is preferably 0.1 to 46 wt. %, more preferably 5 to 37 wt. %. The method of measuring the composition of the organic-inorganic composite material includes secondary ionization mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and observation with an electron probe micro-analyzer (EPMA) or a transmission electron microscope (TEM).
The refractive index of the organic-inorganic composite material can be controlled by changing the amount of the metal element in the organic-inorganic composite material. For example, when the metal element is Si, the refractive index can be decreased by increasing the content of the metal element, while the refractive index can be increased by decreasing the content of the metal element.
When the metal element contained in the organic-inorganic composite material is Si, the metal oxide layer is preferably a silicon oxide layer. By using the same metal element in the organic-inorganic composite material and in the metal oxide layer, the adhesion between the metal oxide layer and the organic-inorganic composite material can be further improved.